Detection of solvent residues in food by gas chromatography

1、 Execution standards

The detection of "No. 6 solvent" in edible oil is aimed at quantitatively analyzing the possible residues of No. 6 light gasoline (mainly composed of low-carbon alkanes such as n-hexane and cyclohexane) in the extraction process of edible oil. The purpose is to ensure the safety of edible oil - No. 6 solvent has volatility and certain toxicity. Long term ingestion of edible oil with excessive residue may cause damage to the nervous and digestive systems. The National Food Safety Standard for Vegetable Oil in China (GB 2716-2018) clearly stipulates that vegetable oil produced by pressing method shall not be detected with solvent No. 6, and the residual amount of solvent No. 6 in vegetable oil produced by leaching method shall be ≤ 10 mg/kg.

2、 Detection principle

The residual solvent No.6 in edible oil was detected using gas chromatography headspace injection method. After heating the sample to gas-liquid equilibrium, the volatile gas was automatically extracted for quantitative and qualitative analysis using the internal standard injection method. The headspace injection was used to select and confirm the chromatographic column and chromatographic conditions. After multiple experiments, the FFAP capillary chromatographic column has the separation ability and symmetrical peak shape.

3、 Preparation method of standard solvent No. 6

1. For vegetable oil, weigh 6 portions of 5.0g (up to 0.01g) base vegetable oil into a 20mL headspace injection bottle. Quickly add 5 μ L of n-hexane standard working solution as an internal standard to each base plant oil (i.e. internal standard content of 68mg/kg), shake gently by hand, and then quickly add 0 μ L, 5 μ L, 10 μ L, 25 μ L, 50 μ L, and 100 μ L of solvent standard with a microsyringe. After sealing, obtain base plant oil standard solutions with concentrations of 0mg/kg, 10mg/kg, 20mg/kg, 50mg/kg, 100mg/kg, and 200mg/kg, respectively. Keep the headspace injection bottle upright and perform rapid circular rotation on a horizontal tabletop to ensure thorough mixing of the substances. During the rotation process, the base vegetable oil should not come into contact with the sealing gasket. If there is any contact, it needs to be reconfigured.

2. For meal types, weigh 3.0g (up to 0.01g) of matrix meal into 6 portions in a 20mL headspace injection bottle, then add 400 μ L of water to each headspace injection bottle, and quickly add 0 μ L, 3 μ L, 9 μ L, 15 μ L, 30 μ L, and 150 μ L of solvent standard with a microsyringe. After sealing, obtain matrix meal standard solutions with concentrations of 0mg/kg, 10mg/kg, 30mg/kg, 50mg/kg, 100mg/kg, and 500mg/kg, respectively. Keep the headspace injection bottle upright and perform rapid circular rotation on a horizontal tabletop to ensure thorough mixing of the substances. During the rotation process, the substrate meal should not come into contact with the sealing gasket. If there is any contact, it needs to be reconfigured.

4、 Sample preparation method

1. Preparation of vegetable oil sample: Weigh 5g (up to 0.01g) of vegetable oil sample into a 20mL headspace injection bottle, quickly add 5 μ L of n-heptane standard working solution as an internal standard to the vegetable oil sample, shake gently by hand, and seal. Keep the headspace injection bottle upright for analysis. During the preparation process, the vegetable oil sample should not come into contact with the sealing gasket. If there is any contact, it needs to be re prepared.

2. Preparation of meal samples: Weigh 3g (up to 0.01g) of meal samples into a 20mL headspace injection bottle, then add 400 μ L of deionized water and seal. Keep the headspace injection bottle upright for analysis. During the preparation process, the substrate meal should not come into contact with the sealing gasket. If there is any contact, it needs to be re prepared

5、 Instrument configuration and analysis conditions

1Detection of solvent residues in food by gas chromatographyoperating conditions

Chromatographic column:

Column furnace: 90 ℃ Injection: 150 ℃ Detection: 150 ℃

Column pressure: 0.05Mpa Tail blowing: 0.05Mpa Split flow: 100ml/min Purging: 5ml/min

2. Headspace injection conditions:

Sample: 80 ℃ Valve box: 70 ℃ Pipeline: 120 ℃

Pressure/Blowing: 0.11Mpa Injection: 0.07Mpa

Placement interval: 5 minutes Sample heating time: 30 minutes

Instrument section:

GC2090 gas chromatograph hydrogen flame detector (FID) logarithmic amplifier

ZKPHS-20A fully automatic headspace sampler with 20 working positions and 200 headspace bottles as a gift

ZKP2000 dual channel (computer, printer self equipped)

Hydrogen air generator integrated machine

High purity nitrogen cylinder 40L nitrogen flow rate 300ml/min

Reagent: Standard solvent No. 6 (brand Zhongkepu)

Pre processing: One ten thousandth electronic balance 1000ml volumetric flask 50ml volumetric flask pipette 0.5ml, 1ml, 2ml, 5ml

Residual solvent curve spectrum

Application scope:Detection of solvent residues in food by gas chromatographySuitable for residual solvents in edible vegetable oil and food processing meal, widely used in edible oil production enterprises, grain and oil processing plants, etc